Except during those many times when he hasn't been, harking all the way back to 1970 and right up to at least the Kennedy-Romney debate of 1994.
To hear this from Romney's own lips...
...scroll down a few inches and click on the video clip.
BTW, for those who don't know, the official position of the Mormon church on abortion, includes exceptions for rape, incest, life of mother and health of mother as determined by a physician of her choice.
2002 - Romney fiercely defends his pro-abortion record since 1970